Circulation: Regulation During Physical Stress, and incorporates more recent findings. The goal is to assist students, physiologists and clinicians to understand control of pressure, vascular volume, and blood flow by examining the cardiovascular system during orthostasis and exercise, two stresses that most affect these variables. These stresses are employed to analyze the passive properties of the vascular system and provide a basis for a detailed examination of how these properties are modified by mechanical, neural, and humoral factors. Interactive effects of the vasculature on cardiac performance are stressed to underline the importance of autonomic control supplemented by muscle pumping to maintain adequate ventricular filling pressure, particularly during exercise. Limitations in cardiac pumping ability, in oxygen diffusion from lungs to blood and from blood to active muscle, in metabolism, and in neural control of organ blood flow are analyzed to explain how total oxygen consumption is limited. The unsolved mystery is the nature of signals that govern the cardiovascular responses to exercise. This is discussed in a new and critical synthesis of ideas and evidence concerning the specific "error signals" that are sensed and then corrected by activation of cardiac and vascular effectors during exercise.

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